A new animal model for retinitis pigmentosa was recently generated by targeted disruption of the inhibitory gamma subunit of rod cGMP-PDE gene (Pdeg). In this proposal, germline gene therapy will first be used to rescue the photoreceptors survival and function. Different mutant PDE-gammas will then be used in attempts to modify photoreceptor function and degeneration. Toward this end, homologous recombination in combination with Cre/lox site-specific recombination will be used to generate mutant alleles in the mouse germ line. These new technologies should allow more temporally- and spatially-controlled expression of mutant PDE-gamma than with traditional transgenic approaches. Selective point mutations engineered in the endogenous PDE-gamma gene locus are predicted to alter the catalytic control of PDE core; the phosphorylation control of PDE-gamma's inhibitory action on the PDE catalytic core; or the binding of the PDE-gamma to transducin. These PDE-gamma mutant lines will yield insights into the mechanism of vertebrate phototransduction in vivo.